64 research outputs found
Dissipation-assisted quantum gates with cold trapped ions
It is shown that a two-qubit phase gate and SWAP operation between ground
states of cold trapped ions can be realised in one step by simultaneously
applying two laser fields. Cooling during gate operations is possible without
perturbing the computation and the scheme does not require a second ion species
for sympathetic cooling. On the contrary, the cooling lasers even stabilise the
desired time evolution of the system. This affords gate operation times of
nearly the same order of magnitude as the inverse coupling constant of the ions
to a common vibrational mode.Comment: 4 pages, 5 figures, substantially revised versio
Correlation inequalities for classical and quantum XY models
We review correlation inequalities of truncated functions for the classical
and quantum XY models. A consequence is that the critical temperature of the XY
model is necessarily smaller than that of the Ising model, in both the
classical and quantum cases. We also discuss an explicit lower bound on the
critical temperature of the quantum XY model.Comment: 13 pages. Submitted to the volume "Advances in Quantum Mechanics:
contemporary trends and open problems" of the INdAM-Springer series,
proceedings of the INdAM meeting "Contemporary Trends in the Mathematics of
Quantum Mechanics" (4-8 July 2016) organised by G. Dell'Antonio and A.
Michelangel
Quantum computation with two-level trapped cold ions beyond Lamb-Dicke limit
We propose a simple scheme for implementing quantum logic gates with a string
of two-level trapped cold ions outside the Lamb-Dicke limit. Two internal
states of each ion are used as one computational qubit (CQ) and the collective
vibration of ions acts as the information bus, i.e., bus qubit (BQ). Using the
quantum dynamics for the laser-ion interaction as described by a generalized
Jaynes-Cummings model, we show that quantum entanglement between any one CQ and
the BQ can be coherently manipulated by applying classical laser beams. As a
result, universal quantum gates, i.e. the one-qubit rotation and two-qubit
controlled gates, can be implemented exactly. The required experimental
parameters for the implementation, including the Lamb-Dicke (LD) parameter and
the durations of the applied laser pulses, are derived. Neither the LD
approximation for the laser-ion interaction nor the auxiliary atomic level is
needed in the present scheme.Comment: 12 pages, no figures, to appear in Phys. Rev.
Generation of long-living entanglement using cold trapped ions with pair cat states
With the reliance in the processing of quantum information on a cold trapped
ion, we analyze the entanglement entropy in the ion-field interaction with pair
cat states. We investigate a long-living entanglement allowing the
instantaneous position of the center-of-mass motion of the ion to be explicitly
time dependent. An analytic solution for the system operators is obtained. We
show that different nonclassical effects arise in the dynamics of the
population inversion, depending on the initial states of the vibrational
motion. We study in detail the entanglement degree and demonstrate how the
input pair cat state is required for initiating the long living entanglement.
This long living entanglement is damp out with an increase in the number
difference . Owing to the properties of entanglement measures, the results
are checked using another entanglement measure (high order linear entropy).Comment: 15 pages, 7 figures, Sub. Appl. Phys. B: Laser and Optic
Quantum computing with four-particle decoherence-free states in ion trap
Quantum computing gates are proposed to apply on trapped ions in
decoherence-free states. As phase changes due to time evolution of components
with different eigenenergies of quantum superposition are completely frozen,
quantum computing based on this model would be perfect. Possible application of
our scheme in future ion-trap quantum computer is discussed.Comment: 10 pages, no figures. Comments are welcom
Grover search with pairs of trapped ions
The desired interference required for quantum computing may be modified by
the wave function oscillations for the implementation of quantum
algorithms[Phys.Rev.Lett.84(2000)1615]. To diminish such detrimental effect, we
propose a scheme with trapped ion-pairs being qubits and apply the scheme to
the Grover search. It can be found that our scheme can not only carry out a
full Grover search, but also meet the requirement for the scalable hot-ion
quantum computing. Moreover, the ion-pair qubits in our scheme are more robust
against the decoherence and the dissipation caused by the environment than
single-particle qubits proposed before.Comment: RevTe
Transport of charged particles by adjusting rf voltage amplitudes
We propose a planar architecture for scalable quantum information processing
(QIP) that includes X-junctions through which particles can move without
micromotion. This is achieved by adjusting radio frequency (rf) amplitudes to
move an rf null along the legs of the junction. We provide a proof-of-principle
by transporting dust particles in three dimensions via adjustable rf potentials
in a 3D trap. For the proposed planar architecture, we use regularization
techniques to obtain amplitude settings that guarantee smooth transport through
the X-junction.Comment: 16 pages, 10 figure
Toward scalable quantum computation with cavity QED systems
We propose a scheme for quantum computing using high-Q cavities in which the
qubits are represented by single cavity modes restricted in the space spanned
by the two lowest Fock states. We show that single qubit operations and
universal multiple qubit gates can be implemented using atoms sequentially
crossing the cavities.Comment: 14 pages, 8 figure
Quantum phase gate with a selective interaction
We present a proposal for implementing quantum phase gates using selective
interactions. We analize selectivity and the possibility to implement these
gates in two particular systems, namely, trapped ions and Cavity QED.Comment: Four pages of TEX file and two EPS figures. Submitted for publicatio
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